I'm thinking about getting a speedlight to use for off-camera lighting, perhaps the SB700, but I don't understand its different wireless triggers, this website says:

For off camera use, the SB700 can be controlled (1) via Nikon’s wireless AWL mode using TTL or manual mode, (2)... or (3) with the simple optical “SU-4″ slave mode.

If I it understand correctly, AWL is not radio, right? so is it necessary to fire the built-in flash to control it, what if I don't want the light from the built-in flash, do I have to use an IR Panel or is there any other to turn off its light only?

I'm also concerned about the optical receiver on the speedlight, apparently it is on right side of the SB700′s body, then how can I position the flash in right side of camera? can the optical receiver still receive the command if it's not positioned in line with camera?

4 Answers
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As Imre said, AWL is an optical wireless protocol, and requires the IR panel to face the on-camera flash for line-of-sight communication.

Getting that IR panel to face the camera is pretty easy: rotate the flash to point the IR panel correctly, then separately turn the flash head to point where you need it. You may have to do some acrobatics with the flash to do this, and something like a Manfrotto Justin Clamp with its small ballhead can be instrumental in getting the correct position.

Experience also says that, depending upon the environment/conditions, you don't quite need line of sight to get the flash to trigger. Using it for a bit you'll find the conditions where it works better or worse, and therefore where radio triggers are a better choice (such as outside in bright conditions, with the flash IR panel facing towards the sun).

AWL/CLS is visible-light based (near-infrared), so yes, the pop-up flash has to fire to communicate with the off-camera flash. However if you set the pop-up flash's power to "--", it does so at a very low power setting, so at normal subject distances, the pulse is unlikely to register in the image over the over-camera flash's illumination. It's liable only to show up at macro distances. At which point, yes, you would need the IR panel to keep the light from showing up in the image.

The "line of sight" requirement of optical systems (and this would be the same for both AWL/CLS and the SU-4 mode slaving), actually isn't a huge deal if you're using the light in studio conditions indoors. The lower ambient light levels, and the availability of bounce surfaces is typically enough to get the master signal's light to the sensor (so long as it's unblocked) without an issue. However, outdoors in bright sunlight, where the mastering signal can be more easily overpowered, then you can achieve line-of-sight by simply rotating the head in a different orientation to the body. This is one of the two reasons why the SB-700's capability to rotate the full 360° is such an asset (the other one being the ability to choose the bounce direction with on-camera bounce).

However, if you're planning on shooting outside or macro the bulk of the time, you may want to consider using add-on radio triggers instead. These days, radio triggers come in a large range of price points and for hobbyist usage, can be quite a bargain. They remove the line-of-sight and range limitations that can sometimes cause optical triggering systems to be frustrating, and you only have to worry about radio interference. :)

Yes, AWL uses flashes to communicate. Not all Nikon cameras can use their built-in flash as a Commander -- that is, can trigger the remote flash. You need to check that the particular model you have will work. (I have a D7100 and it works, though I believe none of the lower-end DX models -- 5300, 3200 -- can operate as a Commander.)

You can set the built-in flash to "off", but it still flashes a little. This would probably only be a problem if you're very close to the subject. If you do have a problem with this, Nikon has an optional IR screen you can purchase that fits on the front of the built-in flash to only allow the IR light through. (AWL depends on the IR part of the flash's spectrum for its communication.)

Yes, AWL is an optical wireless protocol and you have to use IR panel if you use built-in flash as commander. The on-camera flash will trigger on low power in commander mode during exposure even though the camera manual may state it stays off. Alternatively you could use another flash on hot-shoe (you might be able to shield and bounce it so the command signal is not visible on photo) or the SU-800 infrared commander.

You can also use third-party radio triggers, such as PocketWizard or RadioPopper, or the hybrid Aokatec AK-TTL triggers that translate AWL signals on commander into radio signal and back to infrared signal on receiver.